Can you taper the Prozac as well? I don't know if they are capsules or pills that can be halved or quartered. I think withdrawal from Prozac may not be fun at all. That's a decent amount of Prozac to come off of. I don't know but I wouldn't come off that with no taper.
I also would make sure you don't end up taking Prozac with no zyprexa. That could set off a manic episode and it could get ugly.
Also I just want to make sure you have thought this through, and like Venus said you have coping skills to help you out when things get rough. I feel like I remember a pretty depressed post from you about two weeks ago, which would go against your seasonal theory (at least that a light box would help with).
But ultimately it's your choice. I know I would love to be meds free. I also Know it's not an option right now and may not be for a long time. I respect your decision if it's made in the right frame of mind!